Attention-deficit/hyperactivity disorder (ADHD) is a commonly diagnosed behavioral disorder of childhood that represents a costly major public health problem. Despite progress, ADHD and its treatment have remained controversial, especially the use of psychostimulants for both short- and long-term treatment. Although an independent diagnostic test for ADHD does not exist, there is evidence supporting the validity of the disorder. Studies (primarily short-term, approximately 3 months), including randomized clinical trials, have established the efficacy of stimulants and psychosocial treatments for alleviating the symptoms of ADHD and associated aggressiveness and have indicated that stimulants are more effective than psychosocial therapies in treating these symptoms. Because of the lack of consistent improvement beyond the core symptoms and the paucity of long-term studies (beyond 14 months), there is a need for longer-term studies with drugs and behavioral modalities and their combination. Although trials are under way, conclusive recommendations concerning treatment for the long term cannot be made at present. There are wide variations in the use of psychostimulants across communities and physicians, suggesting no consensus regarding which ADHD patients should be treated with psychostimulants, and thus the need for improved assessment, treatment, and follow-up. Furthermore, the lack of insurance coverage, preventing the appropriate diagnosis and treatment of ADHD, and the lack of integration with educational services are substantial barriers and represent considerable long-term costs for society. Finally, after years of clinical research and experience with ADHD, knowledge about the cause or causes of ADHD remain largely speculative. Consequently, there are no documented strategies for the prevention of ADHD.